The active sugar transport in kidney cortex cells will be investigated in vivo (by clearance techniques) and in vitro, using various preparations of renal tissue: 1. Individual pathways of sugar transport will be studied: a. Their structural specificity will be examined with slices, isolated tubules and brush-border membranes using a broad spectrum of model sugars (pentoses, D-glucose, D-galactose, D-mannose, D-fructose, their 2-deoxy-derivatives and methyl-glycosides; commercially not available compounds will be synthesized). The effects of selective inhibitors will be compared. b. The electrolyte re- quirements of the transport pathways, and the coupling between sugar and electrolyte fluxes will be determined. c. The localization of the pathways will be deduced from determinatons of the tissue/plasma ratio in vivo, from the specificity of transport at the antiluminal face of flounder renal tubles, and from the interaction of sugars with brush-border membranes. d. The molecular mechanism of the sugar interaction with membrane components will be studied. 2. The relationship between transport and metabolism of model sugars will be examined: a. The intracellular phosphorylation of sugars will be studied using a newly developed method which allows determination of free and phosphorylated sugars in tissue extracts. b. The interconversion of metabolized sugars by the cells will be investigatedl c. The effects of external pH, Ca2 ion and adenine nucleotides on the sugar transport and metabolism will be studied.